a) Field of the Invention
This invention relates to a scanner-equipped electrophotographic printing machine having a light-emitting and light-receiving head which can perform optical writing on a photoreceptor by an array of light-emitting devices and also reading of an original by an array of light-receiving devices.
b) Description of the Related Art
A scanner-equipped electrophotographic printing machine having a light-emitting and light-receiving head, which can perform optical writing on a photoreceptor by an array of light-emitting devices and also reading of an original by an array of light-receiving devices, has the merit that its optical path becomes shorter compared with a scanner-equipped electrophotographic printing machine making use of a semi-conductor laser. Further, the scanner-equipped electrophotographic printing machine having the light-emitting and light-receiving head also has the merit that no expensive optical system is required and a dimensional reduction is possible. Owing to these merits, a variety of systems have been proposed to date with respect to scanner-equipped electrophotographic printing machines having a light-emitting and light-receiving head.
For example, there is the technique disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 59-12669. According to this technique, a single LED array (an array of light emitting diodes) is commonly used for both writing/reading and illumination of an original. Moreover, it also employs a head assembly constructed of an integral unit of the LED array and a "SELFOC LENS" (trade mark; manufactured by Nippon Sheet Glass Co., Ltd.). Upon writing, the integral head assembly is rotated to a side of a photoreceptor and the LED array is caused to emit light to perform writing. Upon reading, on the other hand, the integral head assembly is rotated to a side of an original and the LED array is caused to emit light to perform reading of the original while illuminating it.
The technique, which is disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 59-12669 referred to above, however has adopted the construction that the head assembly is rotated considerably. An extra space is therefore needed for permitting rotation of the head assembly. This extra space has remained as an obstacle for achieving a dimensional reduction.
Further, a play is indispensable between the head assembly and an associated shaft, about which the head assembly is allowed to rotate, in order to permit smooth rotation of the head assembly. The distance between the photoreceptor and the head assembly however varies due to deformation, wearing and/or vibrations of the shaft. In the case of an electrophotographic printing machine designed to conduct high-density (for example, 600 DPI) printing, the above-mentioned variations result in misregistration or misalignment and blurring of printed dots so that the shaft has remained as a cause for impaired vividness of a picture.